inorganic Chemistry, Vol. 16, No. 10, 1977 2469
Di-p-adeninium-disilver(1) Perchlorate Monohydrate this reaction is largely inhibited for ortho substituents. Acknowledgment. This w o r k was supported by operating grants from the N a t i o n a l Research Council of Canada, which is also t h a n k e d for the a w a r d of a postgraduate studentship
(to J*A+C*)* Matthey and generous loan of iridium.
cO*
is thanked for a
Registry No. 6a, 63731-74-8; 6b, 63731-79-3; 6c, 63731-81-7; 6d, 63731-72-6; 7a, 63731-70-4; 7b, 63731-68-0; 7c, 63731-65-7; 7d, 6373 1-63-5; 8,6373 1-82-8; [Ir(NHNC&I3F)(FBF3)(C0)(PPh3)2]BF4, 6373 1-61-3; [Ir((C6H4F)2N4)(CO)(PPh3)2] BF4, 49732-06- 1; IrH365-33-3; (C0)(PPh3)31 17250-25-8; CF3C6H4N2BF4? 447-59-6; o-FC6H4N2BF43 446-46-8; p-FC6H4N2BF43 19578-37- 1; P - N O ~ C ~ H ~ N 456-27-9. ~BF~, IV and Observed Supplementary Materia’ and calculated structure factors (22 pages). Ordering information is given on any current masthead page.
’-
References and Notes (1) D. Sutton, Chem. SOC.Reu., 4, 443 (1975). (2) R. E. Cobbledick, F. W. B. Einstein, N. Farrell, A. B. Gilchrist, and D. Sutton, J . Chem. SOC.,Dalton Trans., 373 (1977).
(3) A. B. Gilchrist and D. Sutton, J . Chem. Soc., Dalton Trans., 677 (1977). (4) J. Chatt, Nomenclature of “Hydrides of nitrogen and derived cations, anions, and ligands”, private communication of a tentative report of IUPAC.
::{ 2:
~ ~ ~ ~ Ty$%(i$4;;,7 i ~ O ~ ~ ~ ~ f ; (7) A. B. Gilchrist and D. Sutton, Can. J . Chem., 52, 3387 (1974). (8) D. T. Cromer and F. T. Waber, “International Tables for X-Ray Crystallography”,Vol. IV, Kynoch Press, Birmingham, England, 1974. (9) F. W. B. Einstein and R. D. G. Jones, Inorg. Chem., 11, 395 (1972). (IO) F. W. B. Einstein and D. Sutton, Inorg. Chem., 11, 2827 (1972). (1 1) F. W. B. Einstein and D. Sutton, J. Chem. Soc., Dalton Trans., 434 (1973). (12) P. L. Bellon, G. Caglio, M. Manassero, and M. Sansoni, J . Chem. SOC., Dalton Trans., 897 (1974). (13) S. D. Ittel and J. A. Ibers, Inorg. Chem., 14, 636 (1975). (14) E. 0.Schlemper, W. C. Hamilton, and J. J. Rush, J . Chem. Phys., 44, 2499 (1966); M. J. R. Clark, and J. Lynton, Can. J. Chem., 47, 2579 ( 1969). (15) K. R. Laing, S. D. Robinson, and M. F. Uttley, J . Chem. SOC.,Dalton Trans., 2713 (1973). (16) J. A. Carroll, D. R. Fisher, G. W. Rayner-Canham,and D. Sutton, Can. J . Chem., 52, 1914 (1974). ‘(17) S. Trofimenko, J . Am. Chem. SOC.,92, 5118 (1970). (18) S. Trofimenko, Inorg. Chem., 8, 2675 (1969). (19) D. Cashman and F. J. Lalor, J . Organomet. Chem., 32, 351 (1971). (20) R. B. King and M. B. Bisnette, Inorg. Chem., 5 , 300 (1966).
Contribution from the Dgpartement de Chimie, Universitd de Montrbal, Montrgal H 3 C 3V1, P.Q., Canada
Crystal Structure of Di-p-adeninium-disilver(1) Perchlorate Monohydrate CAROLE G A G N O N , JOSEPH HUBERT, ROLAND RIVEST, and ANDRfi L. BEAUCHAMP*
Received March 2, 1977
AIC70159+
Crystals of the title compound belong to space group P2,/c, with a = 15.533 (12) A, b = 7.356 (6) A, c = 13.019 (8) A, fl = 117.43 ( 5 ) O , and Z = 4 monomeric units. They contain planar centrosymmetric [ ( a d e n i n i ~ m ) ~ A g ~cations ] ~ ’ in which two adjacent silver atoms are bridged by two N(3),N(9)-bidentate adeninium cations. N ( l ) is protonated and the acidic proton originally attached to N(9) in adenine is displaced to N(7) in the complex. Each silver atom is coordinated to N(3) of one ligand (Ag-N(3) = 2.194 (10) A) and N(9) of the other (Ag-N(9) = 2.155 (10) A). The distortion at Ag (N(3)-Ag-N(9) = 164.1 (2)O) is ascribed to the arrangement of donor atoms in the ligand. No silver-silver bonding is assumed to exist in spite of the lack of intervening ligand and the relatively short Ag-Ag separation (3.002 (1) A). Perchlorate ions of one type are involved in tridentate interactions with silver atoms: one oxygen in the molecular plane forms a weak ionic bond to silver (Ag-0 = 2.635 (6) A), whereas two more oxy ens interact very weakly by bridging a pair of silver atoms on another complex ion (Ag-0 = 2.903 ( 5 ) and 3.009 (4) ). The water molecule is strongly hydrogen bonded to N(7)-H(7), but all other hydrogen bonds are rather weak. Complex cations and the latter set of perchlorate ions form layers between which another set of weakly hydrogen-bonded perchlorate ions is inserted.
x
Introduction As part of a program of crystallographic studies on silver and mercury complexes with heterocyclic bases of nucleic acids, w e recently reported t h e crystal structure of a silver nitrate complex with 9-methyladenine.’ Those crystals contain infinite chains of digonally coordinated silver ions and bridging N( l ) , N ( 7 ) - b i d e n t a t e ligands. T h e title c o m p o u n d w a s prepared from adenine and silver perchlorate in 2 M HC104. At that acidity, N( 1) and N ( 9 ) would be occupied by protons in the free ligand, which would leave N ( 7 ) and N(3) as potential b i n d i n g sites for silver. H o w e v e r , in multidentate ligands, protons are often transferred to other acceptors by entering metal ions. The crystal structure w a s investigated in order to d e t e r m i n e u n a m b i g u o u s l y t h e distribution of silver and hydrogen ions on the various basic sites available on t h e ligand. Experimental Section Preparation. Adenine (0.70 g) was dissolved in 500 mL of warm water and 54 mL of a 2% AgC104 solution (from AgzO and HC104) was added, followed by 125 mL of concentrated HC10,. On standing in the dark a t room temperature, the mixture yielded 0.20 g of well-formed colorless crystals. Crystal data : formula C5H8AgCl N5O9;fw 460.95; monoclinic; space group P2,/c; a = 15.533 (12) b = 7.356 (6) A; c = 13.019 (8) A; fl = 117.43 ( 5 ) ’ ; v = 1320.3 A3;dcalcd= 2.32 g/Cm3; dobsd =
b;
2.30 g/cm3 (flotation in bromoform-bromobenzene); Z = 4; fi(Mo K a ) = 19.55 cm-I; T = 23 O C ; X(Mo K a ) = 0.710 69 A (graphite monochromator). Crystallographic Measurements. A drawing showing the shape and dimensions of the crystal used is part of the supplementary material. Space group P 2 , / c was indicated from a set of precession photographs. Accurate cell parameters were obtained by refining the setting angles of 15 reflections automatically centered and indexed on a Syntex Pi diffractometer. Intensities of 2340 independent hkl and hk7 reflections within a sphere 26 5 50’ were measured with the P i diffractometer using the 28/8 scan technique. The peaks were scanned from [26(KaI) - l.O]O to [26(Ka2) l.O]O. The scan rate was l o (26)/min for most reflections, but higher rates (up to 24O/min) were automatically selected by the autocollection program for strong reflections. Stationarybackground counts were taken a t each limit of the scan. Counting time was selected to make the background time-to-scan time ratio equal to 0.40. Three standard reflections (310,040,014) measured every 50 reflections showed maximum fluctuations of &3% from average during data collection. Net intensities I were obtained from I = (It - B/0.40)S, where I, is the total scan count, B is the total background count, and S is the scan rate. a(r) was calculated from $(I) = (It B/0.16)S2 (O.02fl2. A total of 476 reflections (including the systematic absences) with I / a ( I ) < 2.5 were considered as “unobserved”. Lorentz and polarization corrections were applied. An absorption correction based on the crystal geometry was applied at a later stage (Program NRC-3,
+
+
+
24'90 Inorganic Chemistry, Vol. 16, No. 10, 1977
Beauchamp et al.
Table I. Refined Atomic Coordinates (x104;for Ag XIO') and Temperature Factors (XlO'; for Ag and C1 X104)a X
Y
Z
37440 (6) -2842 (2) 572 (2) 3100 (6) 4218 (5) -28 (5) 2151 (5) 264 (6) 4364 (7) 2660 (6) 1314 (7) 1477 (7) 541 ( 7 ) -1358 (5) -3721 (6) -4088 (5) -2190 (5) -568 (6) 1564 (6) 1777 (7) -501 (8) -2608 (5)
44820 (3) 3975 (1) 3078 (1) 4591 (3) 4900 (3) 3505 (3) 4186(3) 3800 (4) 4970 (4) 4388(3) 3963 (4) 4089 (4) 3653 (4) 3178(3) 3963 (4) 3663(3) 5129(3) 3258(4) 2040 (3) 4041 (4) 2980 (4) 2410 (3)
C',
1
104570 (2) 4624 (1) 11393 (1) 6872 (2) 8382 (2) 8080 (2) 9200 (2) 6223 (3) 7573 (3) 8453 (3) 7749 (3) 6910 (3) 8943 (3) 4321 (2) 5432 (3) 3836 (2) 4887 (3) 12175 (3) 11112(3) 11666 (3) 10599 (3) 6621 (3)
300 (2) 318 (5) 397 (6) 33 (2) 28 (2) 37 (2) 30(2) 35 (2) 32(2) 28(2) 32(2) 30 (2) 33 (2) 53(2) 5 1 (2) 48(2) 54(2) 66(3) 90(3) 72(3) 80(3) 49 (2)
' ? 2
378 (2) 271 (6) CK1) 355 (6) CK2) NU 39 (2) N(3) 35 (2) N(7) 27 (2) p.J(9) 33 (2) N(10) 45 (3) C(2) 37 (3) ' C(4) 33 (3) C(5) 32(2) c(6) 37 (3) c(8) 37 ( 3 ) O(11) 40(2) O(12) 60(3) W13) 43(2) 0 ~ 4 ) 5 1 (2) O(21) 63 (3) O(22) 60(3) O(23) 70(3) 88 (4) O(24) OW) 42(2) a The form of the anisotropic temperature factor i s e ~ p [ - 2 n ~ ( U , , h ~i aC',,kZb*2 *~ + 2U,, klb*c*)]. Ag
3
495 (2) 388 (6) 377 (6) 4 3 (2) 39 (2) 42 (2) 37(2) 59(3) 42(3) 27 (2) 31 (2) 35 (2) 4 1 (3) 57(2) 75 (2) 55 (29 39 (2) 7 1 (3) 56 (2) 65 (3) 101 (4) 65 (2) U3312c*2+ 2Lr,,hka*b*
+ 2Ul,hla*c* t
Figure 1. Stereoview of [ ( a d e n i n i ~ m ) ~ A g , ]and ~ + its environment. A center of symmetry sits halfway between the silver atoms. All atoms of adenine can be identified by comparison with Figure 2. The formula includes four perchlorate ions: two of type 1, two of type 2. Type 1 ions interact only through hydrogen bonding. Tridentate type 2 anions interact intramolecularly and a total of four anions are required to obtain a complete view of silver environment. Ahmed and Singh). A grid of 10 X 10 X 10 was used and the transmission factor ranged from 0.55 to 0.87. The set of 1864 nonzero reflections was used to solve and refine the structure. Solution and Refinement of Structure. The structure was solved by the heavy-atom method and refined by full-matrix least squares initially and by block-diagonal least squares in the later stages. The function minimized was Cw(lFol - lFc1)2. The silver atom was located from a Patterson map. A subsequent Fourier map revealed the positions of all other nonhydrogen atoms. Isotropic refinement proceeded normally, using unit weights and full-matrix least squares. Silver and chlorine were then refined anisotropically and the R factor (=CllF,,l - IFcll/CIFol) was 0.064. At this stage, the data were corrected for absorption and R was reduced to 0.049. All hydrogen atoms, except those of water, were visible in the difference Fourier map. They were fixed a t their calculated positions (C-H = 0.95 A, N-H = 0.85 A) and were assigned isotropic temperature factors B = 6.0 A2. Individual weights w = ~ / u ( F ) * ~ and block-diagonal least squares were subsequently used. Refinement of the scale factor, secondary extinction ~oefficient,~ coordinates, and anisotropic temperature factors for all nonhydrogen atoms converged to R = 0.031 and R, = (E.w(lF,,l - lFc1)2/wlFo12)'!2 = 0.041. The standard deviation of an observation of unit weight was 1.60. No attempts were made to refine hydrogen parameters. Their positions were recalculated at the end and the new positions were introduced into least-squares calculations. Additional refinement produced no significant changes in the parameters of nonhydrogen atoms. The general background in the final difference Fourier map was lower than f0.5 e/A3, except for two peaks of 0.7 e/A3 near silver. The form factors for nonhydrogen atoms were those of Cromer and Waber.4 The scattering curve of hydrogen was taken from Stewart et Anomalous dispersion factors for silver and chlorine6 were included in the calculations. The computer programs used are listed el~ewhere.~
The refined parameters of nonhydrogen atoms are listed in Table I. Hydrogen coordinates are part of the supplementary material.
escription of the Structure
Two centrosymmetrically related units joined together form a planar [ ( a d e n i n i ~ m ) ~ A gcation ~ ] ~ + in which silver is bonded to N(3) and N(9) of bridging bidentate adeninium ligands. (Figure 1). [Ligand atoms are numbered as in Figure 2 . Cl( 1) and O( lj) with j = 1-4 belong to type 1 perchlorate ions. Atoms of type 2 ions are similarly labeled Cl(2) and O(2j). O(W) is water oxygen.] Interatomic distances and bond angles around silver are listed in Table 11. The unit cell contains two nonequivalent sets of Perchlorate anions. Type 1 anions are remote from silver, and interactions with complex cations are restricted to hydrogen bonding. The pair of silver atoms makes contact with four type 2 anions: two of them form intramolecular bridges above and below the plane of the cation, and two more are found at the ends of the Ag-Ag axis. As noticed for other silver compounds,*-lotwo contiguous silver atoms are nested in a large cavity created by donor atoms of perchlorate ions and adeninium ligands. Coordination of Silver. Each silver atom is surrounded by six neighbors (two nitrogens, three oxygens, and one silver) within 3 A (Table 11) but strong bonds are established only with N(9) (2.16 (1) A) and N(3) (2.20 (1) A). Similar bond lengths have been reported for complexes with imidazole,' pyrazine,I2 9-methyladenine,] and other nitrogen donors.I3 Therefore, silver is basically two-coordinated with an N(3)-Ag-N(9) angle of 164.1 (1)'. Packing is responsible for large departure from linearity in a number of silver
Inorganic Chemistry, Vol. 16, No. 10, 1977 2471
Di-F-adeninium-disilver(1) Perchlorate Monohydrate
Table 111. Effect of Protonation and Metalation on Bond Angles (deg) in the Six-Membered Rinf
N;10
Neutral N(1)-H+ C(5)-C(6)-N(1) C(6)-N(l)-C(2) N(l)-C(2)-N(3) C(2)-N(3)-C(4) N(3)-C(4)-C(5) C(4)-C(S)-C(6)
117.5 118.8 128.8 111.0 126.6 117.2
U
0.6 0.6 Ref 1 Ref 1
Source
N(3)-Cu2+
113.6 (-3.9) 116.8 (-0.7) 123.8 (+5.0) 119.6 (+0.8) 125.2 (-3.6) 127.0 (-1.8) 112.0 (+1.0) 113.5 (+2.5) 127.3 (+0.7) 123.4 (-3.2) 118.0 (t0.8) 119.5 ( t 2 . 3 ) 0.5 Ref 17
N (1)-H+, N(3)-Agt 112.2 (-5.3) 124.8 (+6.0) 124.2 (-4.6) 113.8 (+2.8) 124.8 (-1.8) 120.1 (+2.9) 0.4 This work
a Numbers in parentheses represent differences from the neutral form.
I
N10
Figure 2. Interatomic distances and bond angles in [(adenini~ m ) ~ A g , ] ~Unless +. otherwise stated, esd's are 0.3-0.5' on angles and 0.006-0.007 8, on distances. Table 11. Interatomic Distances and Bond Angles in the Coordination Sphere of Silver and in the Perchlorate Ions Atoms
Dist, A
Atoms N(9)-Ag-N(3)' 2.155 (10) Ag-N(9) N(9)-Ag-O(22)b &-N(3)' 2.195 (10) 3.002 (1) N(9)-Ag-0(23) Ag-0(22)b 3.009 (4) N(9)-Ag-0(24)' N(3)a-Ag-0(22)b Ag-O(23) 2.635 ( 5 ) Ag-O(24)' 2.903 (5) N(3)KAg-0(23) N(3)'-Ag-O(24)' 0(22)b-Ag-0(23) 0(22)b-Ag-0(24)C 0(23)-Ag-0(24)' Cl(l)-O(ll) 1.429 (4) O(ll)-C1(1)-0(12) Cl(l)-O(l2) 1.418 ( 5 ) O(ll)-Cl(l)-0(13) Cl(l)-0(13) 1.430 (4) O(ll)-Cl(1)-0(14) Cl(l)-0(14) 1.445 (4) 0(12)-C1(1)-0(13) 0(12)-C1(1)-0(14) 0(13)-C1(1)-0(14) 0(21)-C1(2)-0(22) Cl(2)-0(21) 1.405 ( 5 ) c1(2)-0(22) 1.417 (4) 0(21)-C1(2)-0(23) c1(2)-0(23) 1.430 ( 5 ) 0(21)-C1(2)-0(24) Cl(2)-0(24) 1.419 (6) 0(22)-C1(2)-0(23) 0(22)-C1( 2)-O(24) 0(23)-C1(2)-0(24) a2-x,1-y,1-z. b X , ' l z - y , ' l z t z . '2-X,'/2 XI2 - z .
Angle, deg 164.1 (2) 88.5 (1) 109.9 (2) 84.4 (2) 81.0 (1) 84.7 (2) 103.0 (2) 106.8 (1) 165.3 (1) 87.8 (2) 109.7 (2) 109.3 (2) 110.0 (2) 110.5 (2) 109.6 (2) 107.6 (2) 109.2 (3) 109.9 (3) 109.3 (3) 110.7 (3) 109.1 (3) 108.6 (3) +y,
complexes.',] ' , I 2 However, in the present case, distortion is most likely due to the ligand geometry and the nearby silver atom. The overall coordination sphere also includes three perchlorate oxygens. The closest to silver is O(23) at 2.635 ( 5 ) A in the molecular plane. Inasmuch as short distances of 2.45 are attained in ionic salts with other oxyanions (nitrate,* c h l ~ r i t e ' ~the ) , Ag-O(23) distance probably corresponds to rather weak ionic bonding. With silver-oxygen distances of 2.903 (5) and 3.009 (5) A, respectively, O(22) and O(24) are just at the 3-A limit where Ag-0 interactions are considered
to become vanishingly small.8 Strictly speaking, they are not bonded to silver, but their particular location with respect to silver and the complex cation suggests nonnegligible Age-0 interactions. The perchlorate ions themselves have the expected tetrahedral structure with only minor distortion. The sixth neighbor of silver is the adjacent silver atom in the dimer at 3.002 (1) A. The Ag-Ag separation is only 0.11 A greater than in metallic silver,I5 but shorter distances have been observed (e.g., 2.88 A in glycine-silver nitratelo). As will be discussed hereafter, metal-metal bonding is not assumed to take place in the present compound. The Ligand. Interatomic distances and bond angles in the ligand are shown in Figure 2. They agree well with the results obtained by de Meester and Skap~ki'~ for (adeninium)2Cu3C18, the only complex reported so far in which complexation takes place at N(3) and N(9) and protonation at N ( l ) and N(7). Protonation and complexation result in considerable changes in the six-membered ring geometry. As shown in Table 111, N ( l ) protonation increases the internal angle at N ( l ) by 5' and decreases the adjacent angles at C(2) and C(6) by 3.5-4.0'. Copper complexation at N(3) in [Cu2(adenine)*(H20)2] (C104)2.2H2017 affects nearby angles similarly but to a lesser extent. Hence, the angle at N(3) undergoes a 2.5' increase, while those at C(2) and C(4) are reduced by 1.8 and 3.2', respectively. The latter effect is also found in the present silver complex and the overall changes (Table 111) correspond approximately to the combined contributions from N ( 1) protonation and N(3) complexation. Surprisingly, in [ (9methyladenine)Ag]NO3.H2O,l ligand geometry was not affected by attachment of silver to N(1). Differences are observed in the five-membered ring geometry with respect to the free ligand, but individual contributions from N(9) complexation and N(7) protonation cannot be sorted out as above. It is interesting to note, however, that the N(7)-C(8) and C(8)-N(9) bond lengths are different in free adenine rings (1.3 10, 1.370 A) but equal in the silver complex (1.332 (4), 1.338 (4) A). This was also noted for copper complexes17 and indicates a redistribution of 7r-electron density and bond order in the N(7)-C( 8)-N(9) section of the molecule. The two-ring system is roughly planar and the distances from the silver atoms to that plane are 0.19 and 0.41 A. Packing. A packing diagram is shown in Figure 3. Packing is frequently controlled by ligand stacking and hydrogen bonding in DNA bases and their metal complexes. In this structure, adjacent dimers are not parallel and stacking effects are totally absent because of the lack of contact between purine rings. On the other hand, Table IV shows only one strong hydrogen bond between water oxygen O(W) and N(7)-H(7) (N-0 = 2.791 (6) A). All remaining distances are much greater than those suggested by Hamilton and Ibers18 for N-H.-0 (2.9 A) and 0-H-0 (2.8 A) hydrogen bonds, and there is no one-to-one correspondence between donors and acceptors. Indeed, in most cases, N-H bonds are directed
2492 Inorganic Chemistry, Vol. 16, No. IO, 1977
Beauchamp et, ai.
Figure 3. Projection of the structure down the b axis. a runs from left to right and c points toward the top of the drawing, [ ( a d e n i n i ~ r n ) ~ A g ~ j ~ + ions and type 2 bridging C1Oc ions form layers parallel to the bc plane at = 0 and 1, whereas type 2 Clod- ions are close to a simiiar plane at a = 'Iz. Table IV. Hydrogen Bond Lengths and Angles
Angle,
Length,
Atoms
d eg
a
N(7)-H(7). ~ O ( W ) N(lO)-H(ll), . .OW) N(lO)-H(2). . .0(11) N(10)-H(2). . .0(14) N(l)-H(l). *0(14)a N(l)-H(1). "O(13)' N(l)-H(l). . *0(12)d O(W)-H. . .O( 14)b O(W)-H. . .0(13)' O(W)-H. ' *0(12)e
153.4 157.7 124.0 146.5 147.3 131.4 121.7
2.791 (6) 3.026 (6) 2.933 (6) 3.024 (6) 2.994 (6) 3.034 (6) 3.074 ( 6 ) 2.954 (5) 2.87 1 (5) 3.05%(6)
8
a l-x,Y,l-z. b x , - l 1 2 - y , - ' / 2 S Z . c-x, d x , 1 i y , z . e 1 - x ,- 1 1 2 + y , l i , - z .
Length from H, a 2.01 2.22 2.37 2.28 2.24 2.40 2.54
+ y , 1i2"-z.
between two potential oxygen acceptors at equal distanses and, conversely, acceptors are equally close to more than one hydrogen atom. Thus, type 1 perchlorates and dimers are not hooked together by well-defined hydrogen bonds. Instead, the edge of the complex ion (including the strongly H-bonded water molecule) looks like a continuous cushion of positively charged hydrogens in contact with negatively charged oxygens of type 1 perchlorate anions. Type 2 perchlorates probably affect packing to a greater extent. Each type 2 ion has two of its oxygens bridging a pair of silver atoms in a dimer, while a third oxygen is bonded to silver atoms in another dimer. Although Ag-O interactions are not particularly strong, the tridentate character of the ion may force a preferred orientation of complex cations in order to place the three silver atoms at positions consistent with its own tetrahedral structure. iscussion Silver was found to react with N(1) and N(7) in [(9methyladenine)Ag]N03.Hz0. However, none of those sites are occupied by silver in the adenine complex described here. Inasmuch as reaction takes place at N(9), a site blocked by a ribose group in DNA, this complex affords little information concerning silver-DNA interactions. However, it raises interesting questions about the distribution of silver and hydrogen ions on the various basic sites available. The amino "lone pair" on N(6) is always involved in the aromatic P system of adenine rings and shows no basic properties. When N(9) is blocked by a ribose (adenosine, AMP, DNA, etc.) or an alkyl group, three potential coordination sites are available. Complexation takes place preferentially on N(7),l9 and in several compounds, N(1) is simultaneously occupied by a proton20 or a second metal ion.is21 Reaction with N ( 1) only is known for one zinc complex,22but no examples of N(3)-coordinated compounds have been reported so far. In adenine, the blocking group is replaced by an acidic hydrogen attached to N(9). Hydrogen remains at that position in ( a d e n i n i ~ m ) Z n C lwhere ~ , ~ ~ zinc binds to N(7), N ( l ) is protonated, and N(3) is free. However, hydrogen displacement from N(9) to N(7), and vice versa, is possible in such ligands. For instance, a hydrogen is attached to N(7) in 6-mercaptopurinez4and transferred to N(9) on binding of
mercury to sulfur in the other ring~25Similarly, in S O ~ E complexes including ours, metal ions bind to N(9) with displacement of hydrogen to N(7)~16 ' 7 , 2 6 , 2 7 Car(II) and M O W Ag(H) are the only metal ions h o w n to react with N(3), and for both, reaction takes place at N(9) as well, With copper, adenine bridging via N(3) and N(9) heads 13 infinite chains in (adeninium)2Cu3C18i6 and to dimers in three other c o m p o ~ n d s . ' ~The ~ * ~copper ~ ~ ~ dimers have much in common with the silver dimer described here. For copper, ( 3 ~ ~ N ( 9 ~ ~ b r ~adenine d g ~ n gligands are around the Cu-Cu axis. With silva, bridging pairs of donors also repeat every 90" around the Ag-Ag axis, but strongly bonded aden alternate with very weakly interacting perchlorate ions. h ends of the metal-metal axis are closed by ligands: perchlorate oxygens in this case, Cl- ions or water molecules in the copper dnmers. The coordinating portion N(3)-C(4)-N(9) of adenine is structurally similar to a carboxylate group, but "bite". Dimers as discussed above are forme acetate,29silver t r i f l u o r ~ a e e t a t eand , ~ ~ carboxyl metah3' y side without intervening ligands raise the problem of metal-metal bonding. The Cu-Cu separation in copper dimers is 0.45 8,greater than in metallic copper and metal-metal bonding is believed to be vanishingly small." However, the Ag-Ag distance observed here is on% greater than in metallic silver (2.89 &.I5 Silversi'lve in thiocarbamates and other compounds has been discusse by Jennische and H e ~ s ewho , ~ ~concluded that metal-mets;i separation (even when shorte termined by ligand geometry r is noteworthy that the Ag-Ag N(3)-Ag-N(9) angle (164.1 ( the expected values (3.08 A, 166"), assuming that the Ions: pairs on N(3) and N(9) are oriented s y ~ m ~ ~ r iwith ca~l~ respect to the adjacent N-@ bonds. e, we do not believe that silver--silver bonding is a ing factor i?; the structure of the present This particular distribution atoms on nitrogens could not be predicted. He factors which may contribute to the stabilization of the structure observed here: (i) the tautomerization energy for hydrogen transfer from N(9) to N(7) is small; (ii) silver atoms bonded to N(3) and N(9) in the direction of the 'lone pairs are separated by a distance greater than in metallic silver; (iii) when pairs of adenine ligands are oriented as observed here, the normal linear two-coordination of silver is achieved with only minor distortion (20° distortions due king forces are not unusual); (nv) two-coordination is ac by nitrogen atoms, for which silvei shows a much greater affinity than for oxygen; (v> when linearly coordinated silver interacts more weakly with extra donor atoms (in the solid state), there are no rigid rules concerning the number and distribution in space o interactions. For instance, in the present compoun nitrogens and three oxygens define an octahedron with one apex missing. The absence of this sixth donor (which would take the place of the other silver) does not break a rigid rule
Novel SO2 Coordination in Rh(NO)(S02)(PPh3)2 in the coordination chemistry of silver and produces no appreciable instability in the compound. All these factors may contribute to various degrees to the stability of the structure observed here. Acknowledgment. We wish to thank the National Research Council of Canada and the MinistZre de 1’Education du Quibec for financial support. We are very grateful to Dr. F. Rochon for permission to use the Syntex diffractometer and valuable assistance during data collection. Registry No. [ ( a d e n i n i ~ m ) ~ A(C104)4-H20, g~] 63301-89-3. Supplementary Material Available: Listings of structure factor amplitudes and H atom coordinates and a drawing showing the shape and dimensions of the crystal used (12 pages). Ordering information is given on any current masthead page.
References and Notes (1) C. Gagnon and A. L. Beauchamp, Znorg. Chim. Acta, 14, L52 (1975); Acta Crustallom.. Sect. E . 33. 1448 (1977). G. H. Stbut andUL. H. Jensen, “X-Ray Struckre Analysis”, Macmillan, New York, N.Y., 1968, pp 420, 457. W. H. Zachariasen, Acta Crystallogr., 16, 1139 (1963). D. T. Cromer and J. T. Waber, Acta Crystallogr., 18, 104 (1965). J. Stewart, R. Davidson, and A. Simpon, J. Chem. Phys., 42,3175 (1965). D. T. Cromer, Acta Crystallogr., 18, 17 (1965). M. Authier-Martin and A. L. Beauchamp, Can.J. Chem.,55, 1213 (1977). P. F. Lindley and P. Woodward, J . Chem. SOC.A, 123 (1966): C. S. Gibbons and J. Trotter, ibid., 2058 (1971). C. J. Gilmore, P. A. Tucker, S. F. Watkins, and P. Woodward, Chem. Commun., 1006 (1969). J. K. H. Rao and H. A. Viswamitra, Acta Crystallogr., Sect. E , 28, 1484 ( 1972). C. J. Antti and K. S. Lundberg, Acta Chem. Scand., 25, 1758 (1971); C. B. Acland and H. C. Freeman, Chem. Commun., 1016 (1971). R. G. Vranka and E. L. Amma, Inorg. Chem., 5, 1020 (1966).
Inorganic Chemistry, Vol. Id, No. 10, 1977 2473 (13) R.L.BodnerandA.I.Popov,Znorg.Chem.,ll,1410(1972);J.E.Fleming and H. Lynton, Can. J . Chem., 46, 471 (1968); R. H. Benno and C. J. Fritchie, Acta Crystallogr., Sect. E , 29, 2493 (1973). (14) J. Cooper and R. E. Marsh, Acta Crystallogr., 14, 202 (1961). (15) “International Tables of X-Ray Crystallography”, Vol. 3, Kynoch Press, Birmingham, England, 1968, p 278. (16) P. DeMeester and A. C. Skapski, J . Chem. SOC.,Dalton Trans., 2400 ( 1972). (17) A. Terzis,A. L. Beauchamp,and R. Rivest, Inorg. Chem., 12,1166 (1973). (18) W. C. Hamilton and J. A. Ibers. “Hydrogen Bonding in Solids”, W. A. Benjamin, New York, N.Y., 1968, p 16. (19) E. Sletten and B. Thorstensen,Acta Crystallogr.,Sect. E, 30,2438 (1974); E. Sletten and M. Ruud, ibid., 31, 982 (1975). (20) A. Terzis, Znorg. Chem., 15, 793 (1976). (21) M. J. McCall and M. R. Taylor, Acta Crystallogr., Sect. E , 32, 1687 (1976); P. DeMeester, D. M. L. Goodgame, A. Skapski, and Z. Warnke, Biochim. Biophys. Acta, 324, 301 (1973). (22) M. J. McCall and M. R. Taylor, Biochim. Biophys. Acta, 390,137 (1975). (23) M. R. Taylor, Acta Crystallogr., Sect. E , 29, 884 (1973). (24) G. M. Brown, Acta Crystallogr., Sect. E , 25, 1338 (1969); E. Sletten, J. Sletten, and L. H. Jensen, ibid., 25, 1330 (1969). (25) P. Lavertue, J. Hubert, and A. L. Beauchamp, Znorg. Chem., 15, 322 (1976). (26) P. DeMeester and A. C. Skapski, J . Chem. SOC.A , 2167 (1971). (27) P. DeMeester and A. C. Skapski, J . Chem. SOC.,Dalton Trans., 424, 1596 (1973). (28) E. Sletten, Acta Crystallogr., Sect. E , 25, 1480 (1969). (29) P. DeMeester, S. R. Fletcher, and A. C. Skapski, J . Chem. SOC.,Dalton Trans., 2575 (1973); G. M. Brown and R. Chidambaram, Acta Crystallogr., Sect. E , 29, 2393 (1973). (30) R. G. Griffin, J. D. Ellett, M. Mehring, J. G. Bullitt, and J. S . Waugh, J . Chem. Phys., 57, 2147 (1972). (31) F. A. Cotton, B. G. DeBoer, M. D. LaPrade, J. R. Pipal, and D. A. Ucko, Acta Crystallogr., Sect. E , 21, 1664 (1971); D. Lawton and R. Mason, J. Am. Chem. SOC.,87, 921 (1965); F. A. Cotton and J. G. Norman, J . Coord. Chem., 1, 161 (1971); M. J. Bennett, K. G. Caulton, and F. A. Cotton, Inorg. Chem., 8, 1 (1969); M. J. Bennett, W. K . Bratton, F. A. Cotton, and W. R. Robinson, ibid., 7, 1570 (1968). (32) P. Jennische and R. Hesse, Acta Chem. Scand., 25, 423 (1971).
Contribution from the Los Alamos Scientific Laboratory, University of California, Los Alamos, New Mexico 87545
Novel Sulfur Dioxide Coordination in Nitrosyl(su1fur dioxide)bis(tripheny1phosphine)rhodium and an Oxygen-18 Study of Its Reaction with Molecular Oxygen’ DAVID C. MOODY* and R. R. RYAN* Received March 16, 1977
AIC70199D
Crystals of Rh(NO)(SO,)(PPh,), have been obtained from SO2-saturated solutions of Rh(NO)(PPh,),, and the structure has been determined a t 25 OC. The compound crystallizes in the orthorhombic space group Pbca with a = 10.338 ( 2 ) A, b = 18.500 (4) A, c = 33.933 (7) A, d, = 1.48 g ~ m - d~, , = 1.47 g ~ m - and ~ , Z = 8 (Cu Kal radiation, X 1.54051 A). The structure refined to an unweighted R value of 0.038 for 2615 reflections with I > 2u(I). The S O 2 binds to the metal both through the sulfur atom and through one oxygen atom with a Rh-S distance of 2.326 (2) 8, and a Rh-O(2) distance of 2.342 (5) A. The S-0(2) distance of 1.493 (5) 8, is considerably longer than the S-O( 1) distance of 1.430 ( 5 ) A, while the 0(1)-S-0(2) angle is 115.1 (4)’. The R h N O unit in this structure is clearly bent with a Rh-NO angle of 140.4 ( 6 ) ” . The factors influencing the bending of the nitrosyl are discussed in terms of the metal coordination geometry and number of d electrons. The mechanism of the reaction of this S,O-bonded SOzwith molecular oxygen to form coordinated sulfate has been studied utilizing oxgen-18 substitution and infrared analysis. This study has revealed a distribution of the labeled oxygen in the resulting Rh(NO)(S04)(PPh3)2different from that observed for S-bonded SO2 reactions with molecular oxygen.
Introduction It is well established that terminally bound SO2can possess both coplanar and pyramidal MS02 geometry when binding to transition metals through the sulfur atom. Likewise, the 0-bonded geometry has been observed in a complex of SO2 with SbF5.2 However, the ability of SOz to bind to transition metals through both the sulfur atom and an oxygen atom simultaneously was not recognized prior to our preliminary communication of the structure of Rh(NO)(SOs)(PPh3)2.’ It
is interesting to note that this type of geometry does appear to be common for both C 0 2 and CS2 and has been structurally established in Ni(C0z)(PCy3)2(Cy = cy~lohexyl)~ and Pt(CS2)(PPh3)2.4 The extreme lability of the SO2 in Rh(NO)(S02)(PPh3)2had been observed previously and had hindered its isolation and characterization. Similarly its reaction with molecular oxygen to form a coordinated sulfate had been r e p ~ r t e d .The ~ significance of these data, however, could only be recognized after the structural features of this
